The preparation of partial or full dentures for a patient is a common dental procedure. Albeit common, the preparation of the denture, or removable prosthetic is a very time consuming and skilled procedure.
Typically, the denture preparation begins by placing a soft impression material, typically an algenate, in a stainless steel standard size impression tray. The material and tray are placed in the mouth of the patient to take an initial impression of the mouth and gumline as the patient bites down into algenate material. The algenate material hardens, and is then used to prepare a preliminary plaster cast of the mouth and gum line.
In the subsequent step, a layer of wax material is molded by hand over the contoured surface of the plaster cast, with a great deal of time and skill required to maintain the wax layer at a uniform thickness as it is molded about the often sharp contours of the preliminary plaster cast. Typically, one will experience thin areas in the wax where it passes over ridges on the cast. Overly thick areas of the wax are often encountered where the wax layer passes over valleys in the cast. Maintaining a uniform thickness in the wax layer is critical to the preparation of the prosthetic, especially along the mouth roof contours, and this uniformity is at present achieved only through the careful and time consuming efforts of a skilled practitioner. A custom impression tray is then fabricated over the preliminary plaster cast and wax sheet. The custom impression tray is most typically formed of a two-part acrylic, including a powder and liquid which harden to form the acrylic when mixed together in a certain ratio. Commonly, the liquid and powder are sprinkled together carefully on the wax sheet and preliminary plaster cast to build up the custom impression tray, again hopefully having a uniform thickness.
When the custom impression tray has been formed, the tray is used to form an even more precise final master cast. An acrylic trial denture base is then made from the final master cast. Wax is then built up on the trial denture base and the prosthetic teeth are positioned in the wax. The base, wax and teeth are placed in the patient's mouth and the teeth and wax manipulated to achieve the proper arrangement. The tray, wax and teeth are then put in a mold filled with liquid plaster under pressure. After the plaster has hardened, the wax is melted out of the mold and the base removed. The wax and base are replaced with acrylic under pressure which bonds to the prosthetic teeth to form the final denture which is perfectly fitted to the patient to ensure the patient's comfort and a secure engagement of the denture to the patient's oral tissues.
Because this procedure is so time consuming and requires such a high level of skill, there is a clear imperative to improve the procedure so that it requires less time and less skill while still achieving a quality product.
While the description and claims that follow exemplify processes for fabricating removable prosthetics (dentures and partial dentures), the advantages and claims are equally applicable to the dental discipline of fixed prosthetics (crowns and bridges) where high accuracy impressions are desirable, and orthodontics where removable acrylic appliances, such as retainers, are fabricated on models or casts of the patient's dentition.